In a number of products, such as energy absorbing structures required in transportation vehicles, it is frequently necessary for a metal foam portion to be attached to formed sheet metal so that a lightweight structure with appropriate resistance and strength is provided which will deform to absorb energy when subjected to an impact. Such attachment may results very expensive to make if the foam portion and the metallic portion need to be separately shaped and then attached to each other.
A useful method for sheet metal forming is provided in “quick plastic” or “superplastic” forming (QPF and SPF) approaches in which sheet metal is formed into a complex shape in a single-sided forming tool using gas pressure to provide the force to form the sheet metal into a shape. In this regard, metal sheets such as particular types of aluminum alloys, titanium alloys, and any other alloy that show superplastic characteristics are heated to characteristic superplastic temperature and then formed into shapes using gas pressure. The technology allows complex shapes to be formed from materials otherwise difficult to form to the complex shape.
What is needed is an approach for providing (a) a composite structure of sheet metal with a metal foam portion produced in a unified operation in such a manner that the foam does not need to be attached after the foam portion has been produced. The present invention is directed to fulfilling this need.